Electrocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid beyond strongly alkaline media: Mechanisms, catalyst design, and scale-up perspectives

The electrocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has attracted considerable interest in biorefinery research because it proceeds under relatively mild conditions and produces a high-value chemical. Although most studies have focused on strongly-alkaline electrolytes, these systems suffer from HMF self-degradation, energy-intensive product separation, and equipment corrosion. Weakly alkaline, neutral, and acidic media offer viable alternatives that can mitigate these drawbacks. This review critically compares different catalyst families, discusses unresolved mechanistic controversies, and evaluates performance and challenges in non-strongly alkaline HMF oxidation reaction (HMFOR). Scale-up and engineering challenges, including membrane selection, local pH control, mass transport, reactor design, and coupled electrolysis, are also discussed. Concept-level materials are distinguished from experimentally validated catalysts and their unresolved drawbacks are explicitly stated. This review aims to guide the rational design of electrocatalysts and support the practical development of non-strongly alkaline HMF electrooxidation.